1. Field of the Invention
This invention relates to disk head assemblies for supporting read/write heads adjacent rotating disks in disk drives and more particularly, to a base plate for attaching a head suspension assembly to a head actuator arm.
2. Description of the Prior Art
In hard disk drives data are stored on magnetizable surfaces of a plurality of rotatable disks that are mounted in a coaxial stack on a housing of the drive. Transducer heads that write data to and read data from the disk surfaces are supported by an actuator that is mounted on the housing and can be actuated to position the transducer heads in alignment with concentric data tracks defined on the disks. Each transducer head is attached to one end of a head suspension that is connected to an actuator arm that extends from the actuator body. The suspensions include a flexible load beam constructed of light sheet steel that has a bend formed in it. The load beam acts as a spring that forces the head against the disk surface with an accurate pre-load or xe2x80x9cgram Loadxe2x80x9d. Air turbulence caused by the rotating disks lifts the heads slightly off of the disks so that the heads fly on an air bearing across the disk surfaces. The air bearing force is counteracted by the suspension gram load.
A head-carrying suspension is attached to an actuator arm using a base plate that forms a part of the head suspension. The base plate includes a flat flange portion and a cylindrical hub portion or boss. The base plate hub is passed through a load beam clearance hole and the flange is spot welded to the load beam. The combined base plate, load beam and a flexure make up a head suspension, and the suspension has the hub of the base plate extending through and beyond the load beam clearance hole.
The hubs of two suspensions are inserted into an actuator arm boss hole formed through an actuator arm extending from an actuator body, one hub entering an actuator arm boss hole from each end of the hole. In the prior art, a swage ball is passed through the cylindrical hubs to force the peripheries of the hubs to expand (swage) into tight engagement with the inner peripheries of the actuator arm boss hole. Thus, an actuator arm may carry two suspensions on opposite sides thereof to support two transducer heads in opposing directions, one up and one down.
Problems with this method of mounting transducer heads have arisen as the need for increased data storage capacity in hard disk drives has grown and the size of the disk drive has decreased to fit in small lap top computers. The problem of forming a strong connection between the actuator arms and the transducer suspensions has been made more difficult as the thickness of the components has become smaller.
Because of the joining of two transducer suspensions to an actuator arm by passing a swage ball through two hubs in the same hole in the actuator arm, an asymmetry exists in the forces that are exerted on the hubs to make the joints. Because the transducer heads face in opposite directions, the hubs on their respective load beams also extend in opposite directions with respect to the direction of passage of the ball through the inner diameters of the hubs. For one transducer suspension, the ball is passed in a direction that tends to place the hub in compressive stress while, for the other transducer suspension, the direction of passage of the ball is such as to tend to place the hub in tensile stress. In order to achieve a permanent bond between the hub and the actuator, the passage of the ball must cause permanent, or plastic, deformation of the hub. This deformation often causes a change in shape of the flange portion of the base plate, which results in a change in the suspension gram load. The differences in shape changes and stresses between the suspensions swaged in tension and compression causes differences in gram load change and hub/actuator joint integrity between these up and down facing parts.
It is therefore an object of this invention to provide a base plate that eliminates the need for swaging and the resulting up and down facing head pre-load and joint integrity differences.
It is also an object of this invention is to provide a base plate that can be is pressed into an a actuator arm to create a press fit.
Briefly, the invention is concerned with a base plate for press fitting into an actuator arm boss hole of a predetermined nominal diameter. The base plate comprises a flange and a hub extending from a region at which the hub meets the flange to an outer end of the hub. The hub has a number of teeth protruding radially outwardly from the hub and extending axially along the hub from the outer end of the hub part way or all the way to the region at which the hub meets the flange.
In accordance with an aspect of the invention, the hub has an outer diameter at the teeth which is greater than the predetermined nominal diameter of the actuator arm boss hole.
The unique base plate geometry reduces tooling and press-in forces, provides a more consistent mating between suspension and actuator, and reduces retention torque sensitivity to actuator hole size variation.
The invention utilizes modified post processing that leaves the base plate with a much higher yield strength than conventionally processed swagable base plates. This increased strength further reduces gram load change caused by the attachment process, increases retention torque, reduces burr formation during press-in, and improves suspension handling damage resistance.
An advantage of this invention is that it allows the use of a base plate to connect a head suspension to an actuator arm without swaging.
The invention has the advantage that press-in base plates reduce the large a stresses and deformations associated with swaging that result in gram load change.
The invention has the further advantage that high integrity joints can be formed between the actuator and head suspension assemblies, even with low hub height base plates.
The invention has the further advantage that press-in base plates eliminate the gram load change difference that occurs between up and down heads resulting from the different mechanics of conventional tension and compression swaging.
The invention has the further advantage that increased flange yield strength results, further reducing gram load change and handling damage sensitivity.